Topics in GC & HPLC

My last two posts have taken us through a couple of topics. Let’s review. First, we welcomed element 112, which was recently christened Copernicium. Then, we pondered the question of why the discoverers couldn’t give it the atomic symbol “Cp.” The answer was that it was already taken by the mysterious element Cassiopeium. Well, as you can see in this post’s doodle, Cassiopeium was what the German-speaking world called element 71 for about 40 years until the IUPAC stepped in to settle the debate, giving the element the name Lutetium (which, by the way, evokes the ancient name for the city that would become Paris, favoring the French claim). Why the dissension? A conflict over primacy of discovery caused the stir, and I find this kind of thing fascinating! You don’t even have to work in a lab to realize that beneath the objective Scientific Method there can seethe human passion, ambition, and pride. Science has its subjective, human side, and that's a necessary element.

You'll note in the picture associated with the post "The Human Element" there was a continuation of the image. I post it here for those interested in seeing the rest of the story...

P.S. The "Welcome to Innovations" was already there. :)

Again, not a directly chromatography-related post, but a follow-up on my previous post (see two below). In that entry I asked why the discoverers of the newly minted Copernicium couldn’t give it the atomic symbol “Cp,” having to use “Cn” instead. I’m sure it’s with bated breath that you await the answer! One of the reasons is that “Cp” was already claimed by an element. A remarkable oversight, right? Now, go and check your periodic table and see if I’m right...I’ll wait (*whistling*)...what’s that you say? No “Cp” either?! What AM I talking about? This is a question I posed my colleagues some months ago with the little doodle you’ll see in this post’s picture. It features our mystery element, Cassiopeium (Cp). I’m no Ed Emberley, but I hope you’ll find the question interesting. The answer involves many of the things I find most exciting about science (great Simpsons quote here), so I hope you’ll stay tuned, and if you know the answer there may be something in it for you!

The MS source temperature is a setting that can be made on an Agilent 7890A/5975C GC/MS. Auto-tunes typically have some sort of default setting. For example a DFTPP specific tune, used for EPA Method 8270, has a default source temp of 230°C. However, if you increase the source temperature, improved peak shape of late eluting analytes such as PAHs results. You may think great! I am going to jack up that source temperature as high as it will go and I will have awesome peak shape. Well, hold on to those horses. Of course all great things come at a cost. The price you pay for better peak shape is stronger fragmentation of your analytes. This could result in a decrease of your quant ion. Check out the figure to see how changing the MS source temp from 230°C to 250°C to 300°C results in better peak shape, but also how it affects 2,4-DNP response. It turns out 250°C looks like the sweet spot for a happy marriage between peak shape and compound response. More 8270? Check out the link below!

So it isn’t chromatography, but as scientists I think we should welcome the newest member of an elite club. I’m talking about the recent official acceptance of Copernicium (Cn) into the pantheon of named elements. Element 112 has been with us for some time (actually, element 112 is never with us for long, being a short-lived, man-made element), but it was only last month that it was given the distinction of a name selected by its discoverers. As you might have guessed, it was named after Nicolaus Copernicus, the famous Renaissance polymath who demonstrated that if you shift your perspective a bit you can see that the universe proper doesn’t actually revolve around us. Pretty dicey stuff for the era, but it paved the way for a bloom of empirical science. This may be apocryphal, but I understand the discoverers originally wanted the atomic symbol to be “Cp.” Anybody know why the IUPAC decided against that? It’s a pretty interesting story! What's in a name? Lots, it turns out.

Today Neil Mosesman and I participated in the PittCon 2010 networking session, Contemporary Food and Environmental Analysis, facilitated by John Mathis of Global Laboratory Services, Inc. John adroitly introduced the topic via slides and then led discussion on challenges faced by analytical chemists, including multiresidue sample preparation methods (e.g. QuEChERS), target/unknown compound instrumental approaches, benefits of triple quad MS versus other mass analyzer systems (like TOFMS), problematic compound analysis (e.g. melamine and cyanuric acid), tobacco analysis (electronic cigarettes!), etc. The discussions were helpful to participants and a good addition to PittCon.

At the end of the session, John was kind enough to allow me to put in a plug for the Florida Pesticide Residue Workshop in July, another excellent forum for similar discussions with many experts in the field, including Steve Lehotay, Michelangelo Anastassiades, Andre de Kok, and others. Please attend!

A recent collaboration with Applied Biosystems used a sensitive LC-MS/MS (4000 QTRAP) with a Restek Ultra Aqueous C18 column as the instrumental determination step for pesticides in QuEChERS extracts of red bell pepper, lemon, spinach, hazelnuts, raisins, and cucumber. Those same QuEChERS extracts were analyzed by a LECO Pegasus 4D GCxGC-TOFMS with Rxi-5Sil MS and Rtx-200 columns. Becky Wittrig of AB related preliminary data today at PittCon in a well-attended afternoon lecture.

We are still processing data, but one thing was clear, this red bell pepper was subject to multiple uses of pesticides as seen by the residues found using LC-MS/MS (see figure). Similar results were seen for GCxGC-TOFMS, except where the pesticides were not GC-able (e.g. thiamethoxam, clothianidin, spinosyn). But GCxGC-TOFMS also located endosulfans, endosulfan sulfate, and permethrins, compounds not ionizable using electrospray. Conclusion: both GC and LC are very important in pesticide analysis.

Yesterday (Sun, Feb 28) in Orlando, FL, my colleague Scott Grossman gave an excellent PittCon 2010 presentation on split liner performance. Contrary to widely published information on the web, not all split liners perform equally (or even as advertised!). Eventually there will be a webinar available at restek.com for this presentation. Until then, consider using a Precision liner for split injection. It provides a low-discrimination, accurate, and precise (1-2% RSD typical) split injection, and is very low cost compared to other, more sophisticated liners that may or may not perform as well.

I also want to provide a tip of the hat to Corby Hilliard at Restek, who helped with much of the data collection for the presentation. I believe this may be his first co-authorship of a PittCon presentation, so congrats on that. And, I know he is working on a new parallel dual-column solution for GC-ECD analysis of EPA Method 8095 explosives. Wait until you see his fantastic HMX peak!

The title is akin to “Free Beer” to get you to click in, but I invite my colleagues to visit me and Restek at PittCon. Due to space limitations, I only tout my presentations here (yeah right Jack, it’s because of space limitations...). I’m heavily invested in QuEChERS. Poster 660-2 P, Mon, comparing GPC to cartridge SPE cleanup of dietary supplement QuEChERS extracts. Thu, 10:35, Room 308D, I talk on QuEChERS and GCxGC-TOFMS for dietary supplement pesticides. On Wed, 2:00, Room 307B, 2230-1, come see “Who Stole Selectivity from Gas Chromatographers and Can We Get It Back?”

Finally, it is a pleasure to work with Becky Wittrig (former Restek star!) and Andre Schreiber of Applied Biosystems on a QuEChERS pesticides-in-food project that Becky framed as a battle of GC versus LC! She will be giving the 1590-7 talk Tue, 4:15, Room 309AB (waitaminute... did she get a bigger room than me?). A big NOD to Julie, Jason, and Michelle for contributing to this project! And Aqueous C18!

Acetonitrile injections don’t damage Rxi-5Sil MS GC columns. But urban legends persist, so analysts sometimes do unnecessary and laborious solvent exchanges for QuEChERS extracts.

A real problem that might warrant solvent exchange is mismatch between the polar solvent acetonitrile and non-polar pesticide GC columns (e.g. DB-5ms, Rxi-5Sil MS). Upon injection, lack of wetting leads to split GC peaks, especially severe for early eluters. Adjusting GC oven start temperatures rarely eliminates the problem.

A simple method for avoiding split GC peaks for acetonitrile extracts is to add toluene to the extract. At 50% toluene, peak splitting is gone, and sensitivity is only reduced by 2 (not even that, considering height reduction of split peaks). Even 25% toluene can eradicate peak splitting. Adding internal standard in toluene to a QuEChERS extract prior to injection is an elegant way to kill two European Starlings with one Accrington brick. And, no solvent exchange!